More to the point, human's reproductive lifetime is usually about 30 years. So by the time you realize that you've fucked up your society, the cohort that could do something about it has now aged out of childbearing years. You're left with a much smaller cohort to fix the problem, but because there are now so many fewer women of childbearing age, increases in fertility rate lead to many fewer births.

This is actually happening with Millennials. Strauss and Howe predicted a "Crisis of 2020" that would lead to civic renewal and presumably a higher birth rate, but it now appears that 2020 was the beginning of the crisis and it won't be resolved for some time, perhaps a generation, and by that time Millennials (globally, the last big generation) will have aged out of childbearing years. Any baby boom will be led by late Zoomers, at best, and that's a small generation that's already affected by the collapse in birth rates.

My takeaway: the globalized, technologically advanced society we have now is doomed to collapse, and we should be working hard to take that advanced technology and identify simplified versions of it that can be run and maintained by a much smaller, localized workforce.